In the field of arc welding, the main types of welding processes are gas-metal arc welding with solid (GMAW) or metal-cored wires (GMAW-C), gas shielded flux-cored arc welding (FCAW-G), self shielded flux-cored arc welding (FCAW-S), shielded metal arc welding (SMAW) and submerged arc welding (SAW). Of these processes, gas metal arc welding with solid or metal-cored electrodes are increasingly being used for joining or overlaying metallic components. These types of welding processes are becoming increasingly popular because such processes provide increased productivity and versatility. Such increase in productivity and versatility results from the continuous nature of the welding electrodes in gas metal arc welding (GMAW & GMAW-C) which offers substantial productivity gains over shielded metal arc welding (SMAW). Moreover, these electrodes produce very good looking welds with very little slag, thus saving time and expense associated with cleaning welds and disposing of slag, a problem that is often encountered in the other welding processes. In submerged arc welding, coalescence is produced by heating with an electric arc between a bare-metal electrode and the metal being worked. The welding is blanketed with a granular or fusible material or flux. The welding operation is started by striking an arc beneath the flux to produce heat to melt the surrounding flux so that it forms a subsurface conductive pool which is kept fluid by the continuous flow of current. The end of the electrode and the work piece directly below it become molten, and molten filler metal is deposited from the electrode onto the work. The molten filler metal displaces the flux pool and forms the weld. In shielded metal arc welding, shielding is obtained by a flux coating instead of a loose granular blanket of flux. In flux-cored electrodes, the flux is contained within the metal sheath.
In the art of welding, much prior effort has been expended in developing flux compositions of the type having predetermined flux components intended to perform in predetermined manners. A large number of compositions have been developed for use as fluxes in arc welding both for use generally as welding fluxes and for use as a coating on a metallic core or within a sheath. Fluxes are utilized in arc welding to control the arc stability, modify the weld metal composition, and provide protection from atmospheric contamination. Arc stability is commonly controlled by modifying the composition of the flux. It is therefore desirable to have substances which function well as plasma charge carriers in the flux mixture. Fluxes also modify the weld metal composition by rendering impurities in the metal more easily fusible and providing substances which these impurities may combine with in preference to the metal to form slag. Other materials may be added to lower the slag melting point, to improve slag fluidity, and to serve as binders for the flux particles.
One problem encountered with welding with stick electrodes is the resultant porosity of the weld metal, especially at the beginning of the welding process. At the start of the weld process using a stick electrode, the heat transferred to the tip of the electrode is initially relatively low and then increases rapidly. As a result, at the start of the welding process, some of the stick electrode melts and is transferred to the workpiece to begin the formation of a weld bead. Although the initial heating of the tip of the electrode is sufficient to melt the internal wire rod of the stick electrode, the initial heat is insufficient to heat the coating sufficiently on the electrode, which coating provides a shielding gas during the welding operation. The shielding gas generated by the coating produces an environment about the weld metal that inhibits or prevents oxygen and nitrogen from dissolving in the weld metal, which dissolved gases may subsequently be expelled from the weld metal during the cooling of the weld bead. The expulsion of these gasses from the weld metal can result in porosity in the weld metal which in turn can result in an inferior weld bead. As a result, at the beginning of the welding process, the metal transferred to the workpiece can have an unacceptable amount of porosity which can result in a reduction in the weld bead quality. U.S. Ser. No. 10/840,701 filed May 6, 2004, which is incorporated herein by reference, discloses one type of stick electrode to address the porosity problems associated with stick electrodes.
Another problem encountered with welding with stick electrodes is weld puddle control at the beginning of the welding process. This is especially a concern when welding in the vertical down position. Typically, the welding wire does not easily melt at the beginning of the welding process, thus the quality of the weld bead is less acceptable at the start of a welding process.
In view of the problems of weld bead porosity and weld puddle control at the start of welding when using prior art stick electrodes, there remains a need for a stick electrode that forms a high quality weld bead throughout the welding process.